How are language and culture related?

Language and culture are very closely related. They are inseparable. A language is the vehicle by which a culture is passed on from parents to children. A language is an essential part of a culture.
As a child absorbs his/her culture, he/she aquires the language of the culture. These two things happen at the same time, and you rarely have one without the other.

For the most part, there is one language and one language only for each culture. A country with two languages generally has two different cultures - Belgium is an example.

Learning a language as an adult means that you acquire some of the culture that goes with it. It is very hard to learn a language without picking up some of the culture. Taking an interest in the culture makes it easier to learn the language of the culture. Living within the culture makes it even easier.

Learning a new language as an adult doesn't completely change the way you see the world, but it does give you another way of looking at the world. A language doesn't shape the way you think. A language expresses the way a culture thinks and categorizes things. If a language has no word for "three" or higher numbers, it's because the culture sees no need to count higher than two. A person who lives in a culture with no word for "three" doesn't think it's necessary to count over 2, and when shown 5 items will not remember that there are 5 because the culture doesn't think it's important to count that high. It's not the language which blocks the memory of 5 - it's the culture. One's culture shapes the way one thinks.

Some people seem to think that a person can not remember that there are 5 items because there is no word for 5 in one's language. Wrong. It is because the person's culture does not see a need for counting items above 4.

Language learned as an adult does not shape thought. Culture shapes thought; the thoughts are expressed in language.

Some languages make distinctions that others don't. English distinguishes between "I'm speaking" and "I speak". (I'm speaking English to you right now vs I speak Spanish and Italian) Spanish generally doesn't make that distinction, but can if it wants to. (Te hablo en inglés ahora vs hablo español y italiano) English speakers think it's more important to make that distinction, and Spanish speakers know that you will have no problem understanding what is meant, but can emphasize the distinction if they feel it's necessary. (Te estoy hablando en inglés)
If your language has no word for dark blue it's because your culture doesn't feel it's necessary to make the distinction between "blue" and "dark blue."
If someone shows you different shades of blue you call them all blue because your culture thinks they are all blue.
Your language doesn't shape your ability to distinguish shades of blue - your culture does, and you acquired your culture through your language as a child.

If English is your native language, you will probably have trouble with Polish and Russian verb tenses. They work very differently from English tenses. Learning Polish or Russian well implies getting how the tenses work. Once you understand how the culture views verb actions, you will get the tenses. You picked up some Russian culture by learning Russian tenses. If you want to speak Polish or Russian correctly, you have to understand how the tenses work.

A language learned as an adult does not impose on its speaker a picture of reality. The culture does. The culture was transmitted to the person when he/she was a child through the language. The child learned the culture concurrently with the language.

Learning a new language opens a person to a different culture, different words and different concepts. Learn Greek and see what kefi, filotimo and filoxenia mean.
Learning a new language won't change your world-view, but it will open you up to understanding other cultures' world views.

Some are confused over this. This confusion comes from thinking that a language is an abstract entity, separate from the people who speak it, and from the culture that it is part of, and that it expresses. A less analytical approach is closer to the truth.